Active-set management based on an associated codec

ABSTRACT

Embodiments may involve the adjustment of the way in which coverage areas are included in the active set of a wireless communication device (WCD), based on the codec that is currently associated with the WCD. An illustrative method involves a radio access network (RAN): (a) determining a codec that is associated with a WCD; (b) using the associated codec as a basis for determining a value for at least one active-set parameter for the WCD; and (c) sending a message to the WCD, wherein the message indicates the determined value for the at least one active-set parameter.

RELATED APPLICATION

This patent application is a continuation of U.S. patent applicationSer. No. 13/693,934, filed on Dec. 4, 2012, the contents of which areentirely incorporated herein by reference, as if fully set forth in thisapplication.

BACKGROUND

To provide cellular wireless communication service, a wireless serviceprovider or “wireless carrier” typically operates a radio access network(RAN) that defines one or more coverage areas in which WCDs can beserved by the RAN and can thereby obtain connectivity to broadernetworks such as the public switched telephone network (PSTN) and theInternet. A typical RAN may include one or more base transceiverstations (BTSs) (e.g., macro network cell towers and/or femtocells),each of which may radiate to define a cell and cell sectors in whichWCDs can operate. Further, the RAN may include one or more base stationcontrollers (BSCs) (which may also be referred to as radio networkcontrollers (RNCs)) or the like, which may be integrated with orotherwise in communication with the BTSs, and which may include or be incommunication with a switch or gateway that provides connectivity withone or more transport networks. Conveniently with this arrangement, acell phone, personal digital assistant, wirelessly equipped computer, orother wireless communication device (WCD) that is positioned withincoverage of the RAN can then communicate with a BTS and in turn, via theBTS, with other served devices or with other entities on the transportnetwork.

Wireless communications between a WCD and a serving BTS in a givencoverage area will typically be carried out in accordance with one ormore agreed air interface protocols that define a mechanism for wirelessexchange of information between the WCD and BTS. Examples of suchprotocols include CDMA (e.g., EIA/TIA/IS-2000 Rel. 0, A (commonlyreferred to as “IS-2000” or “1×RTT”), EIA/TIA/IS-856 Rel. 0, A, or otherversion thereof (commonly referred to as “IS-856”, “1×EV-DO”, or“EVDO”)), iDEN, WiMAX (e.g., IEEE 802.16), LTE, TDMA, AMPS, GSM, GPRS,UMTS, or EDGE, and others now known or later developed.

The air interface protocol will generally define a “forward link”encompassing communications from the BTS to WCDs and a “reverse link”encompassing communications from WCDs to the BTS. Further, each of theselinks may be structured to define particular channels, through use oftime division multiplexing, code division multiplexing (e.g.,spread-spectrum modulation), frequency division multiplexing, and/orsome other mechanism. The forward link, for example, may define (i) apilot channel on which the RAN may broadcast a pilot signal to allowWCDs to detect wireless coverage, (ii) system parameter channels (e.g.,a sync channel) on which the RAN may broadcast system operationalparameters for reference by WCDs so that the WCDs can then seek networkaccess, (iii) paging channels on which the RAN may broadcast pagemessages to alert WCDs of incoming communications, and (iv) trafficchannels on which the RAN may transmit bearer traffic (e.g., applicationdata) for receipt by WCDs. And the reverse link may define, for example:(i) access channels on which WCDs may transmit “access probes” such asregistration messages and call origination requests, and (ii) trafficchannels on which WCDs may transmit bearer traffic for receipt by theRAN.

In a conventional CDMA wireless network compliant with the IS-2000standard, each cell employs one or more carrier frequencies, typically1.25 MHz in bandwidth each, and each sector is distinguished fromadjacent sectors by a pseudo-random number offset (“PN offset”).Further, each sector can concurrently communicate on multiple differentchannels, distinguished by “Walsh codes.” In doing so, each channel isallocated a fraction of the total power available in the sector. When aWCD operates in a given sector, communications between the WCD and theBTS of the sector are carried on a given frequency and are encoded bythe sector's PN offset and a given Walsh code.

Wireless service providers typically design their wireless networks tocomprise a number of partially-overlapping wireless coverage areas. As aWCD that is subscribed to a wireless service provider moves about, thewireless network may hand off the WCD from one wireless coverage area toanother. A goal of performing such handoffs is to provide asubstantially continuous wireless coverage to the WCD, so that anycommunication sessions conducted by the WCD are not dropped or degradeddue to loss of wireless coverage. Further, to facilitate handoffs, a WCDmay have an “active set” of coverage areas (e.g., sectors) that it canbe handed off to.

In another aspect, for certain types of communication, such as voicecalls, video calls, and/or other types of calls, a WCD may be able touse two or more different types of codecs when engaging in suchcommunication. However, each codec may have different characteristicsthat impact the extent of resources used when the WCDs arecommunicating.

OVERVIEW

In an exemplary embodiment, a wireless communication device (WCD) maysupport various types of codecs. These codecs may define how mediacontent (e.g., voice, music, still images, and/or video) are encoded anddecoded. Different codecs may have different features. For instance, avoice codec used by a WCD might encode and decode digital voice at arate of 1 to 15 kilobits per second. However, to achieve these bitrates, some of the information present in an input analog voice signal(e.g., high-frequency spectral components) may be lost when digitized.Thus, codec design can be a tradeoff between achieving a low bit ratefor a particular type of media (which is desirable to conserve networkand storage capacity) and the user-perceived quality of the mediaproduced by the codec, which typically improves as more bandwidth isutilized.

Herein, a characterization of the quality provided by a codec should beunderstood to indicate the quality of the media produced by that codec.For instance, a “high-quality codec” should be understood as being acodec that generally produces media of a higher quality (as compared tosome other codec that generally produces media of a lower quality).

There may be various scenarios where a radio access network (RAN)assigns a codec to a given WCD, such as during call setup and/or whenpaging a WCD. When the RAN assigns a codec, the RAN may select from twoor more different codecs that are supported by the given WCD. Sincewireless spectrum is limited, it may benefit wireless network operatorsto allocate wireless resources judiciously, and codec selection andassignment is an opportunity to do so. Therefore, when multiple codecsare supported by a particular WCD, a RAN may be configured to considervarious factors when determining which codec to assign to the WCD, suchas factors indicating the utilization of network resources in the sectorwhere the WCD is located.

It may be desirable for a WCD not to be handed off from a coverage areawhere it currently is assigned, or is likely to be assigned, ahigh-quality codec. Accordingly, exemplary embodiments may involve a RANand/or a WCD managing a WCD's active set with this purpose in mind. (Ofcourse, it should be understood that this purpose is not limiting, andexemplary embodiments may be implemented with other purposes in mind.)

For example, certain parameters may affect the number of coverage areasthat are included in a WCD's active set and/or the ease with which acoverage area can be added to and/or removed from the active set, may inturn affect the probability of the WCD being handed off. Herein, suchparameters may be referred to as “active-set parameters.” Accordingly,an exemplary embodiment may involve a RAN and/or a WCD adjustingactive-set parameters so as to reduce the probability of a handoff whenthe WCD is associated with a higher-quality codec. On the other hand, aRAN and/or a WCD may adjust active-set parameters so as to increase theprobability of a handoff when the WCD is associated with a lower-qualitycodec, in hopes that the WCD will be assigned a higher-quality codec ina different coverage area.

In one aspect, an exemplary method involves a RAN: (a) determining acodec that is associated with a WCD, (b) using the associated codec as abasis for determining a value for at least one active-set parameter forthe WCD, and (c) sending a message to the WCD, wherein the messageindicates the determined value for the at least one active-setparameter.

In another aspect, an exemplary RAN system may include a non-transitorycomputer-readable medium and program instructions stored on thenon-transitory computer-readable medium. The program instructions may beexecutable by at least one processor to: (a) determine a codec that isassociated with a wireless communication (WCD), (b) use the associatedcodec as a basis to determine a value for at least one active-setparameter for the WCD, and (c) send a message to the WCD, wherein themessage indicates the determined value for the at least one active-setparameter.

These and other aspects and advantages will become apparent to those ofordinary skill in the art by reading the following detailed description,with reference where appropriate to the accompanying drawings. Further,it should be understood that the foregoing overview is merely forpurposes of example and is not intended to limit the scope of theinvention as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

An exemplary embodiment of the present invention is described hereinwith reference to the drawings, in which:

FIG. 1 is a simplified block diagram of a wireless communicationnetwork, according to an exemplary embodiment;

FIG. 2 is a simplified block diagram showing functional components of aradio-access-network component, according to an exemplary embodiment;

FIG. 3 is a flow chart illustrating a method 300 that may be implementedby a radio access network, according to an exemplary embodiment;

FIG. 4 shows a table that includes data indicating, for various codecs,a corresponding setting for a maximum-active-sector parameter, acorresponding T_ADD setting, and a corresponding T_DROP setting,according to an exemplary embodiment; and

FIG. 5 is a flow chart illustrating a method that may be implemented bya wireless communication device, according to an exemplary embodiment.

DETAILED DESCRIPTION

Exemplary methods and systems are described herein. It should beunderstood that the word “exemplary” is used herein to mean “serving asan example, instance, or illustration.” Any embodiment or featuredescribed herein as “exemplary” is not necessarily to be construed aspreferred or advantageous over other embodiments or features. Theexemplary embodiments described herein are not meant to be limiting. Itwill be readily understood that certain aspects of the disclosed systemsand methods can be arranged and combined in a wide variety of differentconfigurations, all of which are contemplated herein.

It should be noted that the term “handoff” is to be interpreted broadlyherein. Thus, a WCD being “handed off” from a one wireless coverage areato another wireless coverage area may include scenarios in which: (i)the WCD is participating in communication via a first coverage area whena handoff to another coverage area occurs, (ii) the WCD is notparticipating in communication via a first wireless coverage area whenthe handoff occurs, and (iii) the WCD is engaged in a call via a firstcoverage area, the first call is terminated, and soon after the WCDengages in a second call via a second coverage area.

I. EXEMPLARY COMMUNICATION NETWORKS

Referring to the drawings, as noted above, FIG. 1 is a simplified blockdiagram of a wireless communication network in which an exemplary methodcan be implemented. It should be understood, however, that this andother arrangements described herein are set forth only as examples. Assuch, those skilled in the art will appreciate that other arrangementsand elements (e.g., machines, interfaces, functions, orders, andgroupings of functions, etc.) can be used instead, and that someelements may be omitted altogether. Further, many of the elementsdescribed herein are functional entities that may be implemented asdiscrete or distributed components or in conjunction with othercomponents, and in any suitable combination and location. In addition,various functions described herein as being performed by one or moreentities may be carried out by hardware, firmware, and/or software. Forinstance, various functions may be carried out by a processor executingprogram instructions stored in memory or another machine-readable medium(i.e., data storage, rather than a mere signal), to achieve, forinstance the useful, concrete, and tangible result of helping to improvethe paging success rate in an access network.

As shown in FIG. 1, the exemplary network includes at its core a radioaccess network (RAN) 12 that radiates to define numerous coverage areasin which wireless communication devices (WCDs) can engage in RFcommunication with the RAN. The RAN may define these coverage areasdiscretely through use of directional antennas and/or by variousmodulation parameters, including, without limitation, carrierfrequencies and PN offsets or other parameters, depending on the airinterface protocol used. Example air interface protocols include CDMA(e.g., IS-95, IS-2000, 1×RTT, 1×EV-DO, etc.), iDEN, WiMAX, TDMA, AMPS,GSM, GPRS, UMTS, EDGE, LTE, WI-FI (e.g., 802.11), BLUETOOTH, and othersnow known or later developed. In practice, the coverage areas mayoverlap to some extent, so that a served WCD can move seamlessly fromone coverage area to another.

As shown, the RAN may include numerous base stations (also known as basetransceiver stations or BTSs), designated in the figure as base stations14-30 and one or more base station controllers 50 (which may beintegrated with one or more of the base stations). The base stationspreferably include directional antennas, power amplifiers, andassociated transceiver equipment arranged to establish correspondingwireless coverage areas to communicate with WCDs in those coverageareas. The coverage areas can be cell sites, cell sectors, or some otherdefined wireless coverage area (possibly even a combination of coverageprovided by multiple base stations).

Each base station controller may be coupled with one or more switches,such as a mobile switching center (MSC) 52, which provides connectivitywith the public switched telephone network (PSTN) 54, so that servedWCDs can communicate with remote entities 56 on the PTSN. Additionallyor alternatively, each base station controller may be coupled with oneor more gateways, such as packet data serving node (PDSN) 58, whichprovides connectivity with a packet-switched network 60, so that servedWCDs can communicate with remote entities 62 on the packet-switchednetwork.

In general, a RAN 12 may take various forms and may include any of avariety and number of components, depending for instance on the airinterface protocol employed by the RAN. As such, the RAN 12 may vary indegree of complexity, from a simple wireless access point router to amore complex system such as that shown for instance. Further, it shouldbe understood that actions that are generally described as being carriedout by the RAN (or simply by the “network” or a “wireless communicationnetwork”) may be carried out by various different entities orcombinations of entities in the RAN, possibly in conjunction with otherentities in communication with the RAN. It should also be understoodthat features and functionality described in reference to one networkentity or combination of entities, such as a BTS, BSC, MSC, and/or PDSN,may also be carried out by other entities without departing from thescope of the invention. Yet further, note that the combination of BTS104 and BSC 106 may be considered a base station. However, BTS 104 orBSC 106 could, taken alone, be considered a base station as well.Additionally, a base station may be considered to be either or both ofthose devices, and perhaps make use of one or more functions provided byan MSC, a PDSN, and/or any other entity.

FIG. 1 depicts a representative WCD 64 by way of example, which could bea cell phone, wirelessly equipped personal digital assistant (PDA), orany other type of wirelessly-equipped device now known or laterdeveloped. The WCD is preferably equipped with hardware, software,and/or other logic to communicate with RAN 12 in accordance with anagreed communication protocol, such as one of the protocols noted hereinfor instance. For example, in an exemplary embodiment, WCD 64 includes awireless communication interface that functions to facilitate airinterface communication with RAN 12 according to one or more protocolssuch as those noted above. Further, WCD may include a user interface,which typically includes components for receiving input from a user ofWCD and providing output to a user of the WCD. Yet further, WCD 64 mayinclude program logic stored in data storage (e.g., one or more volatileand/or non-volatile storage components of the WCD, such as magnetic,optical, or organic storage components) and executable by one or moreprocessors (e.g., general purpose and/or special purpose processors) tocarry out various functions described herein.

Each WCD, such as WCD 64, typically has at least one associatedidentifier that uniquely identifies the WCD. By way of example, a WCDmay have a unique mobile directory number (MDN), a unique InternationalMobile Subscriber Identity (IMSI), a unique MAC address, or some otheridentifier dynamically or statically assigned to the WCD, which mayserve as its address for receiving air interface communicationstransmitted to it by the RAN. As a specific example, an IMSI is a uniquenumber associated with the WCD, typically taking the form of the WCD'sphone number. Additionally or alternatively, each WCD may be assigned amobile identification number (MIN).

To keep track of where WCDs, such as WCD 64 are operating, a RAN 12 mayinclude a visitor location register (VLR) 68 and a home locationregister (HLR) 66, as shown in FIG. 1. VLR 68 may include informationrelated to WCDs that are currently being served by MSC 52, while HLR 66may include information related to all WCDs that utilize RAN 12.

In a further aspect, each WCD may have a service profile stored in theHLR 66 and/or in the VLR 68 that corresponds to the MSC 52 that iscurrently serving a WCD 64. Each MSC 52 may be coupled to the HLR 66 andor its VLR 68 by an out of band signaling network such as a SignalingSystem #7 (SS7) network, for instance, and may thus access the serviceprofile for a WCD using an identifier for the WCD, such as its MIN, MDN,and/or IMSI.

VLR 68 and/or HLR 66 may obtain information regarding the locations ofWCDs through registration messages that the WCDs transmit at varioustimes. For example, a WCD might transmit a registration message thatidentifies its current cell-sector when the WCD first powers-up, atregular time intervals thereafter (e.g., every 10 minutes), and inresponse to other triggers (such as moving a certain distance or movinginto a different paging zone). These registration messages could bereceived by VLR 68 and HLR 66. In this way, VLR 68 and HLR 66 maymaintain location for each WCD in its service area (which could be, forVLR 68, the area served by MSC 52 and, for HLR 66, all areas served byRAN 12). The location information for a WCD could include anidentification of the cell-sector that the WCD reported in its mostrecent registration message and the date/time of the most recentregistration message. HLR 66 and/or VLR 68 could also maintain othertypes of location information for WCDs.

II. EXEMPLARY RAN COMPONENT

FIG. 2 is a simplified block diagram showing functional components of aRAN component 201, according to an exemplary embodiment. RAN component201, which could be a base station or a switch, for example, or couldtake another form. As shown, the RAN component 201 may include an RFcommunication interface 200, a backhaul interface 202, a processor 204,and data storage 206, all of which may be communicatively linkedtogether by a system bus, network, or one or more other connectionmechanisms 208.

In practice, RAN component 201 may take the form of or include one ormore BTS and/or a BSC, such as BTSs 18-24 and/or BSC 50 for instance, ormay take the form of a switch, such as MSC 52. Accordingly, theillustrated components of RAN component 201 (e.g., communicationinterface 200, a backhaul interface 202, a processor 204, and datastorage 206) may be distributed and/or subdivided between one or moreBTSs, a BSC, and/or an MSC, or may be implemented in a single BTS, asingle BSC, or a single MSC. It should be understood that an exemplarysystem may also take the form of another network entity or combinationsof other network entities, without departing from the scope of theinvention. Further, an exemplary system may be implemented in orprovided in communication with a base station (or implemented in orprovided in communication with any other network entity or entitiesarranged to carry out analogous functions).

In RAN component 201, RF communication interface 200 may comprise one ormore antenna structures, one or more power amplifiers, and associatedequipment, for engaging in RF communication with WCDs operating withinthe base station's coverage, according to one of the air interfaceprotocols noted above for instance. Backhaul interface 202 may compriseany sort of communication link or mechanism enabling the base station toexchange signaling and bearer data with other RAN entities, such as withMSC 52 for instance. Processor 204 may comprise one or more processors(e.g., general purpose and/or special purpose processors), such asmicroprocessors for instance. And data storage 206 may comprise one ormore volatile and/or non-volatile storage components, such as magnetic,optical, or organic storage components, integrated in whole or in partwith processor 204. As further shown, data storage 206 preferablycontains program logic 210 (e.g., machine language instructions)executable by processor 204 to carry out various functions, such as thefunctionality of the exemplary methods and systems described herein.

III. EXEMPLARY CODECS

A RAN 12 and/or a WCD 64 may use various types of codecs to encodeand/or decode a voice call and/or other types of communications. A codecmay encode an analog or digital stream of information (e.g., voice,video, still images, music, data, and so on) for transmission and/orstorage. For example, a source WCD may include a voice codec thatreceives a spoken utterance from a user, and encodes this utteranceaccording to a particular format. The source WCD may then transmit theencoded utterance to a destination WCD. The destination WCD may includethe same (or a similar) voice codec to decode the utterance from theparticular format so that the destination WCD can play out the resultingsignal.

In general, there may be a roughly linear relationship between codec bitrate and the media quality (e.g., the voice quality) that the codecproduces at that bit rate. For example, a voice codec operating at 9.6kilobits per second is likely to produce better quality voice than avoice codec operating at 4.8 kilobits per second. However, as codectechnologies advance, new codecs may be introduced that are capable ofsupporting equal or better media quality at a lower bit rate. Thus, insome cases, a voice codec that operates at 8.5 kilobits per second mayproduce better voice quality than the voice codec operating at 9.6kilobits per second. Furthermore, some voice codecs are capable ofsupporting multiple different encoding rates, and perhaps even switchingbetween these rates dynamically to adapt to the characteristics of theinput signal and/or to achieve a target bit rate.

In order to further illustrate these aspects of codecs, severaldifferent voice codecs are compared and contrasted below. In anexemplary embodiment, CDMA wireless networks may use one or more codecsfrom the Enhanced Variable Rate Codec (EVRC) family.

For instance, the EVRC-A codec operates on input speech signals sampledwith 16-bit resolution 8,000 times per second (i.e., a sampling rate of8,000 Hz). The resulting 128 kilobit per second stream is divided into20 millisecond frames, each of which is compressed to either 171 bits(8.55 kilobits per second), 80 bits (4.0 kilobits per second), or 16bits (0.8 kilobits per second). EVRC-A may also be referred to as CMDAservice option 3.

The EVRC-B codec also operates on input speech signals sampled with16-bit resolution 8,000 times per second, and supports the threecompressed bit rates supported by EVRC-A. However, EVRC-B also supportsa compressed frame size of 40 bits (2.0 kilobits per second).Additionally, EVRC-B supports eight operating points, each defining atarget bit rate. When configured to operate at one of these operatingpoints, EVRC-B may attempt to achieve the desired bit rate by switchingbetween two or more of the supported frame sizes. EVRC-B may also bereferred to as CMDA service option 68.

The EVRC-WB codec is a “wideband” variation of EVRC-B. Particularly,EVRC-WB operates on input speech signals sampled with 16-bit resolutionat 8,000 or 16,000 times per second. When sampling at the rate of 8,000times per second, frames encoded with EVRC-WB can be compatible withEVRC-B encodings. When sampling at 16,000 times per second, framesencoded with EVRC-WB are 171 bits (8.55 kilobit per second). However,unlike the 171 bit frames produced when sampling at 8,000 times persecond, the EVRC-WB frames include high-frequency components from the3.5 kHz to 7 kHz range. Thus, at the same bit rate, EVRC-WB may becapable of producing higher quality voice calls than EVRC-A or EVRC-B.Additionally, EVRC-WB supports two of the operating points of EVRC-B,and also supports a mode for improved encoding of non-speech signals,such as music-on-hold. EVRC-WB may also be referred to as CMDA serviceoption 70.

The EVRC-NW codec, which may also be referred to as CMDA service option(SO) 73, supports some of the encodings of both EVRC-B and EVRC-WB.Particularly, EVRC-NW supports the sampling rates and frame sizes ofEVRC-WB. Also, EVRC-WB supports seven of the operating points of EVRC-B,and also supports the mode for improved encoding of non-speech signals.Thus, EVRC-NW is fully compatible with EVRC-WB, and supports moreoperating modes of EVRC-B than EVRC-WB.

To support both EVRC-B and EVRC-WB, EVRC-NW includes eight capacityoperating points (COPs), which may be referred to as EVRC-NW COP 0 toCOP 7, or simply as COP 0 to COP 7. Under EVRC-NW, COP 0 is a rate 1wideband voice encoder. Further, EVRC-NW COP 4 is a narrowband voiceencoder as defined under EVRC-B. EVRC-NW COPs 1 to 3 are narrowbandvoice encoders that provide higher voice quality as compared to EVRC-B,with COP 1 providing the greatest improvement over EVRC-B. Further,EVRC-NW COPs 5 to 7 are narrowband voice encoders that provide lowervoice quality as compared to EVRC-B, with COP 5 being the closest toEVRC-B in quality.

In an exemplary embodiment, a RAN 12 may be configured to determinewhich codec or codecs are supported by a given WCD, and to assign one ofthe supported codecs to the WCD to use for a given communication. TheRAN 12 may determine the codec or codecs that are supported by aparticular WCD in various ways. For example, when a WCD 64 originates acall, the WCD 64 may transmit an origination message to the RAN 12. Thisorigination message may include an indication of the service optionssupported by the WCD 64. For instance, the origination message mayinclude the WCD's preferred service option (e.g., service option 73) aswell as one or more auxiliary service options (e.g., service option 3and/or service option 68) that the WCD also supports.

Further, for a WCD receiving a call (e.g., a callee WCD), the RAN maystore or have access to a profile that includes indications of theservice options supported by the WCD. This profile may also specify theWCD's preferred service option as well as one or more auxiliary serviceoptions that the WCD also supports. Thus, for an incoming call to acallee WCD, the RAN may receive an indication that a call has arrived atthe RAN for the callee WCD, access the profile of the callee WCD todetermine the supported codecs, and based on various factors discussedin more detail below, determine which codec to assign to the callee WCDfor the call.

In some embodiments, the HLR and/or the VLR may indicate the serviceoption capabilities for individual WCDs that have registered with theRAN. For example, the HLR and/or VLR may indicate that a particular WCDis configured for SO 73. In an exemplary embodiment, this may beinterpreted as implying that the particular WCD is capable of using anyof COP 1 to COP 7, and that a base station (e.g., a BTS), may negotiatewhether the particular WCD is capable of COP 0 (i.e., HD Voice).

As such, before a BTS 18 pages a WCD 64 for a voice call, the BTS maycoordinate with its serving MSC to access the VLR and determine whichservice options are supported by the WCD 64. Further, when a WCD thatsupports EVRC-NW (i.e. SO 73) acknowledges a page by sending the RAN 12a page response message, the WCD may also indicate the particularoperating points that are supported by the WCD in the page responsemessage.

In an exemplary embodiment, a BTS may consider various factors whendetermining which codec should be assigned to a WCD for a given call.For example, in some embodiments, the BTS may consider the utilizationof at least part of the RAN infrastructure. If the utilization of awireless coverage area serving the WCD, a wireless coverage area that islikely to serve the WCD, a BTS, a BSC, and/or a backhaul link betweenany RAN and/or non-RAN components is too high, it may be preferable toinstruct the WCD to use a codec with a lower expected bit rate, such asEVRC-A or EVRC-B. However, if this utilization—or utilizations—is nottoo high, it may be preferable to allow the WCD to use a codec thatsupports a higher expected bit rate, and thereby potentially increasingthe media quality of the call. In this latter case, the BTS may instructthe WCD to use a codec with a higher expected bit rate, such EVRC-NW COP0 or COP 1.

Once the RAN (e.g., a BTS) has assigned a codec to a WCD to use for acall, the RAN may notify the WCD of the assigned codec. For example,according to SO 73, a base station may send the WCD a Service OptionControl message that includes the particular operating point that isassigned to the WCD for the call (e.g., one of COP 0 to COP 7). Otherexamples are also possible.

In some embodiments, a RAN may attempt to assign EVRC-NW COP 0 to allWCDs that support COP 0, unless the utilization of network resources ina coverage area is too high. This may be done in an effort to provideWCDs with the best call quality that is possible, and/or for otherreasons. In the event that the utilization is too high, then the RAN mayselect a codec that provides lower quality, such as one of EVRC-NW COPs1 to 7.

Determining whether the utilization is “too high” may be based on one ormore utilization thresholds. For instance, the RAN may measure theutilization of a wireless coverage area serving the WCD and compare themeasured utilization to a utilization threshold. If the measuredutilization exceeds the utilization threshold, the RAN may instruct theWCD to use EVRC-B. Otherwise, the RAN may instruct the WCD to useEVRC-WB or EVRC-NW. The utilization threshold may be represented as apercentage, such as 30%, 40%, 50%, 60%, 70%, and so on.

It should be understood that the codecs described herein are onlyexamples. Other voice or non-voice codecs may be used instead.

IV. EXEMPLARY HANDOFF FUNCTIONALITY

In an exemplary RAN 12, a WCD 64 may be in communication with one ormore wireless coverage areas simultaneously, even if the WCD is onlyactively using one of these wireless coverage areas to communicate.

Receiving signals from multiple wireless coverage areas simultaneouslymay provide advantages for a WCD. For instance, doing so allows the WCDto keep track of neighboring wireless coverage areas that are candidatesfor a handoff. Regularly, or from time to time, the WCD may measure thestrength of the signals received from each wireless coverage area. Thesesignals may be received on a traffic channel, a paging channel, or someother type of channel, and the measurements may involve determining thesignal-to-noise ratio (SNR) and/or the frame error rate (FER) of thesignals.

When a WCD is served by a given wireless coverage area and determinesthat the signal strength the WCD received from this given wirelesscoverage area has dropped below a signal-strength threshold, the WCD mayrequest a handoff from the given wireless coverage area to a newwireless coverage area from which the WCD has received a higher signalstrength. The WCD may also request a handoff to a new wireless coveragearea when the received signal strength of the new wireless coverage areaexceeds that of the given wireless coverage area by some amount. As aresult of measuring this received signal strength and using thesemeasurements to influence handoff behavior, continuity of wirelessservice may be improved. For instance, the WCD may be handed off fromthe given wireless coverage area before it experiences a poor signalstrength from the given wireless coverage area that substantiallycompromises the WCD's ability to communicate.

In an exemplary embodiment, a WCD 64 may be configured to maintain an“active set” that can include multiple sectors (with each includedsector being referred to as an “active sector”). A WCD 64 may monitorthe signal strength of the active sectors, as well as other sectors thatare not in its active set, so that it can request that sectors be addedto and/or dropped from the active set.

The RAN may provide a WCD 64 with settings for parameters that help theWCD determine when to request that sectors be added to and/or droppedfrom its active set. For instance, under IS-2000, a base station mayprovide a WCD the following parameters, which relate to pilot signalstrength and are used by the WCD to maintain its active set:

-   -   T_ADD: Threshold pilot strength for addition to the active set        (e.g., −14 dB).    -   T_COMP: Threshold difference in signal strength from an active        set pilot (e.g., 2 dB).    -   T_DROP: Threshold pilot strength for removal from the active set        (e.g., −16 dB).    -   T_TDROP: Time for which an active set pilot falls below T_DROP        to justify removal from the active set (e.g., 2 seconds).        The base station also provides the WCD with a Neighbor List        Update Message (NLUM), which identifies the “neighbor” sectors,        which are not in the active set, but have been identified as        candidates for the active set.

The WCD 64 then scans for all of the pilot signals from the sectors inits active set, and measures the received signal strength for each. Forexample, WCD 64 may calculate Ec/Io for each sector in the active set,where Ec is energy per chip and Io is the total power received. If thepilot signal strength of any neighbor sector exceeds T_ADD, the WCD 64adds the pilot to its “candidate” set and sends a Pilot StrengthMeasurement Message (PSMM) to the base station with the estimated Ec/Iofor the pilot and information indicative of the identity of the sector.

Further, if the pilot strength exceeds the strength of any active-sectorsignal by T_COMP (and possibly also depending on current capacity andother issues), then the base station may send a Handoff DirectionMessage (HDM) to the WCD, listing the pilot as a new member of theactive set. Upon receipt of the HDM, the WCD 64 then adds the pilot toits active set as instructed, and the WCD sends a Handoff CompletionMessage (HCM) to the base station (e.g., to BTS 108), acknowledging theinstruction, and providing a list of the pilots (PN offsets) in itsactive set. Depending on system configuration, the WCD may also identifypilot signals from the remaining set of sectors that exceed thethresholds. It should be understood that each active sector in theactive set is represented by its corresponding PN offset, and thatreferences to an active sector may also be considered to refer to the PNoffset of the active sector.

Similarly, if the WCD 64 detects that the signal strength of a pilot inits active set drops below T_DROP, the WCD starts a handoff drop timer.If T_TDROP passes, the WCD then sends a PSMM to the base station,indicating the Ec/Io and drop timer. The base station may then respondby sending an HDM to the WCD, without the pilot in the active set. TheWCD would then receive the HDM and responsively move the pilot to itsneighbor set and send an HCM to the base station.

Under IS-2000, a WCD 64 may continually scan its active sectors,neighbor sectors, and candidate sectors in a cyclical manner, accordingto a schedule under which active sectors are scanned twice as frequentlyof neighbor sectors, and neighbor sectors in turn are scanned twice asfrequently as candidate sectors. The details of this scanning processare generally known to those skilled in the art, and thus not discussedin further detail herein. Further, when the WCD 64 is engaged in IS-2000communications, WCD 64 typically decodes transmissions using all the PNoffsets in its active set, together with the respective Walsh codesassigned for each PN-identified sector. Then, on a frame-by-frame basis,the WCD may select a sector from its active set from which to receiveforward-link traffic.

In a further aspect, a WCD 64 and/or a RAN 12 may be configured tomanage the active set of a WCD 64 using a number of techniques.

For instance, an exemplary WCD 64 may be configured vary the maximumnumber of active sectors that are permitted in the active set byupdating a maximum-active-sector parameter, which indicates the maximumnumber of active sectors that are allowable in the active set. As anexample, the WCD may by default set a maximum-active-sector parameter tothree, in which case up to three sectors may be included in the activeset and scanned as active sectors. However, the WCD 64 may adjust themaximum number of active sectors by setting the maximum-active-sectorparameter to six, for instance, in which case up to six sectors may beincluded in its active set. Other adjustments to the maximum number ofactive sectors are also possible.

Further, the RAN 12 may determine a value for the maximum-active-sectorparameter of a particular WCD 64, and then send an instruction to theWCD 64, which indicates that the WCD 64 should adjust itsmaximum-active-sector parameter accordingly. As such, a WCD 64 may beconfigured to adjust its maximum-active-sector parameter upon beinginstructed to do so by the RAN.

Note that there is no requirement that a WCD actually include themaximum number of active sectors in its active set. This maximum numbershould therefore be understood as a constraint on the active set, butnot necessarily a requirement. As such, it is possible that, at a givenpoint in time, less than the maximum number of sectors meet the criteriafor the active set, and as a result, less than the maximum number ofsectors will be included in the active set.

In addition or in the alternative to adjusting the maximum-active-sectorparameter, an exemplary WCD may be configured to adjust a number ofparameters affecting whether a sector is included in the active set,either alone or in combination with each other. For example, a WCD 64and/or a RAN 12 may be configured to adjust the value of T_ADD, T_COMP,T_DROP, and/or T_TDROP in an effort, for example, to change theprobability that a WCD will add a given sector to its active set and/orto change the probability that an active sector is kept in the activeset. Further, the RAN 12 may be configured to determine a value for eachof one or more of T_ADD, T_COMP, T_DROP, and/or T_TDROP, which should beused to manage a given WCD's active set. In the event that the RAN 12determines that a WCD 64 should adjust one or more such parameters, theRAN 12 may send an instruction to the WCD 64 which indicates how the WCD64 should adjust such parameters.

To implement some or all of the above functionality (and othermobile-station functionality described herein), an exemplary RANcomponent may include a tangible computer-readable medium with programinstructions stored thereon, which are executable by a processor tocarry out the various functions described herein. For example, anexemplary base station or switch may include program instructions thatare executable to: (a) determine a codec that is associated with awireless communication (WCD), (b) use the associated codec as a basis todetermine a value for at least one active-set parameter for the WCD, and(c) send a message to the WCD, wherein the message indicates thedetermined value for the at least one active-set parameter. Otherexamples are also possible.

Additionally or alternatively, to implement some or all of the abovefunctionality (and other mobile-station functionality described herein),an exemplary WCD may include a tangible computer-readable medium withprogram instructions stored thereon, which are executable by a processorto carry out the various functions described herein. For example, anexemplary WCD may include program instructions that are executable to:(a) determine a codec that is assigned to the WCD, (b) use the assignedcodec as a basis for determining a value for at least one active-setparameter for the WCD, wherein the at least one active-set parameteraffects how many active sectors that are included in an active set ofthe WCD, and (c) manage the active set of the WCD according to the atleast one active-set parameter.

V. EXEMPLARY RAN-IMPLEMENTED METHODS

An exemplary method may be carried out by a RAN component in an effortto reduce the likelihood of a handoff when the WCD is assigned ahigher-quality codec, or, conversely, in an effort to increase thelikelihood of the WCD handing off when the WCD has been assigned ahigher-quality codec. In particular, the WCD may a codec that waslast-assigned, or that is about to be assigned, to the WCD, and then usethis codec as a basis for managing the active set of the WCD. Anexemplary method may be carried out for other reasons as well, withoutdeparting from the scope of the invention.

For example, FIG. 3 is a flow chart illustrating a method 300 that maybe implemented by a RAN, according to an exemplary embodiment. It shouldbe understood that references herein to RAN performing variousfunctions, such as those of method 300, encompass a component of a RAN,such as a base station or an MSC, carrying out the various functions.Further, an exemplary method or portions thereof may be carried out byanother entity or a combination of entities, without departing from thescope of the invention.

According to method 300, the RAN determines a codec that is associatedwith a given WCD, as shown by block 302. The RAN may then use theassociated codec as a basis for determining a value for at least oneactive-set parameter for the WCD, as shown by block 304. The RAN canthen send a message to the WCD, which indicates the determined value forthe at least on active-set parameter, as shown by block 306.

A. Determining the Codec that is Associated with a Device

i. Determining the Last-Assigned Codec

In some embodiments, block 302 may involve the RAN determining the codecthat was last assigned to the WCD, which may be referred to as thelast-assigned codec. More specifically, if the WCD was recently assigneda certain codec in a coverage area, it may be taken as an indicationthat the WCD is more likely to be assigned that codec for a new call inthat coverage area. Accordingly, if the last-assigned codec for a WCD ina certain coverage area provides for a higher-quality voice call, thenthis may be interpreted as an indication that the WCD is likely to beassigned a higher-quality codec for a new call. Accordingly, the RAN mayapply less concatenation (or possibly no concatenation) to a page to aWCD for a new call, if the last-assigned codec for the WCD was ahigh-quality codec, and vice versa. By doing so, the RAN may increasethe likelihood that a page is successful, when there is a greaterlikelihood that the target WCD will be assigned a higher-quality codec.

In a further aspect, a RAN may also consider the “staleness” of thelast-assigned codec when determining the value for the at least oneactive-set parameter. More specifically, if less time has elapsedbetween the assignment of the last-assigned codec and a page toestablish a new call, then the last-assigned codec may be considered abetter indicator of the codec that is likely to be assigned for the newcall. Accordingly, block 306 may involve the RAN using the elapsed timesince the assignment of the last-assigned codec as a further basis fordetermining the value for the at least one active-set parameter. Forexample, the RAN may only change the value of an active-set parameterwhen the elapsed time is less than a threshold period of time. On theother hand, if the elapsed time is greater than the threshold period oftime, then the RAN may simply use a default value for the active-setparameter.

In some embodiments, some or all of method 300 may be carried by a basestation in a RAN. In order to determine the codec that was last assignedto a given WCD, at block 302, a base station may reference a codecdatabase that is maintained by or otherwise accessible to the basestation. For example, a base station can maintain a codec database thatindicates the last-assigned codec or codecs for particular WCDs inparticular coverage areas. Accordingly, whenever a base stationinstructs a WCD to use a certain operating point under EVRC-NW, the BTSmay store a record of the operating point that is assigned to the WCD(e.g., one of EVRC-NW COPs 0 to 7), as well as an indication of thecoverage area (e.g., the cell ID or sector ID) in which the operatingpoint that is assigned to the WCD. Thus, before base station pages aWCD, the base station may access the codec database to determine thelast-assigned codec for the WCD in the coverage area where the basestation is about to page the WCD.

In a further aspect of some embodiments, base stations may be configuredto send indications of codecs that are assigned to their respectiveserving switches, so that the switches can readily determine the lastassigned codec for a given WCD. In particular, when a base stationassigns a codec to a WCD, the base station may send a message to itsserving switch that indicates the WCD to which the codec was assigned,the specific codec that was assigned to the WCD, and possibly otherinformation, such as the time of assignment. The switch may then updatethe VLR and/or the HLR with this information. For example, the VLRand/or HLR may include last-assigned-codec data that indicates, on aper-WCD basis, one or more codecs that were most recently assigned toeach WCD (and the order in which the codecs were assigned, if multiplecodecs are indicated for a given WCD). Additionally or alternatively,the last-assigned-codec data for a given WCD may indicate the mostrecently assigned codec in each of two or more coverage areas.Accordingly, the switch may access the VLR and/or the HLR to determinethe last-assigned codec for a WCD, possibly on a per-coverage-areabasis.

ii. Determining the Currently-Assignable Codec

In some embodiments, block 302 may involve the RAN determining a codecthat is currently assignable to the WCD in a given coverage area. Forinstance, method 300 may be implemented by a RAN during a callorigination process or during a call, when a switch or a base station isabout to assign or has just assigned a codec to the WCD for the call. Insuch an embodiment, block 302 may simply involve the RAN assigning acodec to a WCD based at least in part on network utilization in thecoverage area where WCD is connected for the call and/or based on otherfactors. Method 300 may then be carried out to update at least oneactive-set parameter based on the assigned codec.

In particular, during a call-origination process, a RAN may determine acodec to assign to a WCD that is involved in the call, as shown by block302. The WCD may be, for example, the WCD that initiated the call (e.g.,a source WCD), or a WCD to which the call is being directed (e.g., atarget WCD). The RAN may then use the codec as a basis for determining avalue for at least on active-set parameter for the WCD, as shown byblock 804. Further, the RAN may send a message to the WCD, whichindicates the determined value for the at least one active-setparameter, as shown by block 306.

Note, however, that the RAN does not need to determine thecurrently-assignable codec during a call origination process or anongoing call. Rather, in some embodiments, the RAN may determine acurrently assignable codec even when there is no codec assigned or aboutto be assigned to a WCD. For instance, RAN may determine a codec thatwould be assigned to a WCD if, for example, a call were to be initiatedat that time. To do so, the RAN may select a codec in the same way itwould if it were assigning a codec to the WCD (e.g., based on networkutilization), but refrain from actually assigning the codec.

B. Determining Active Set Parameter(s) for a WCD Based on the AssociatedCodec

In some embodiments, block 304 may involve the RAN determining a valuefor a maximum-active-sector parameter. For instance, on an exemplaryembodiment, the RAN may decrease the value of the maximum-active-sectorparameter for higher-quality codecs, and increase the value of themaximum-active-sector parameter for lower-quality codecs.

By reducing the maximum number of active sectors when the WCD isassigned a higher-quality codec, the RAN may reduce the likelihood ofthe WCD handing off to another coverage area, where it might be assigneda lesser-quality codec. Conversely, by increasing the maximum number ofactive sectors when the WCD is assigned a lower-quality codec, the RANmay increase the likelihood of the WCD handing off to another coveragearea, where it might be assigned a higher-quality codec

In some embodiments, there may be a number of different codecs that areavailable for the RAN to assign to a WCD, which include at least a firstand a second codec. Further, the first codec may provide forhigher-quality voice service as compared to the second codec. Morespecifically, if the WCD is associated with the first codec, then theRAN may set the value of the maximum-active-sector parameter equal to afirst value. If the WCD is associated with the second codec, then theRAN may set the value of the maximum-active-sector parameter equal to asecond value. Further, since the first codec is of higher quality thanthe second codec, the second value may be greater than the first value.Thus, when the WCD is assigned the higher-quality codec, the WCD isaccordingly instructed to set its maximum-active-sector parameter to thelower first value. Setting the maximum-active-sector parameter to thelower value may result in less sectors being included in the active set,and thus may decrease the probability that the WCD hands off from asector where it is assigned a higher-quality codec, to another sectorwhere it might be assigned a lower-quality codec.

As another example, consider again a scenario where there are a numberof different codecs that are available for assignment to WCDs. In thiscase, the available codecs may include one or more first codecs, one ormore second codecs, and one or more third codecs, where the one or morefirst codecs provide higher-quality voice service as compared to the oneor more second codecs, and where the one or more second codecs providehigher-quality voice service as compared to the one or more thirdcodecs. Thus, if the associated codec is one of the first codecs, thenthe RAN may set the value of the maximum-active-sector parameter to afirst value. If the associated codec is one of the second codecs, thenthe RAN may set the value of the maximum-active-sector parameter to asecond value that is greater than the first value. And, if theassociated codec is one of the third codecs, then he RAN may set thevalue of the maximum-active-sector parameter to a third value that isgreater than the second value.

In a specific implementation of the above example, the one or more firstcodecs may be EVRC modes 0 to 2, the one or more second codecs may beEVRC modes 3 to 4, and the one or more third codecs may be EVRC modes 5to 7. Accordingly, the maximum-active-sector parameter may be set to alower number of sectors when the associated codec is one of EVRC modes 0to 2, than when the associated codec being is one of EVRC modes 3 to 7.Further, when the associated codec is one of EVRC modes 3 to 4, themaximum-active-sector parameter may be set to a higher number of sectorsthan when the associated codec is one of EVRC modes 0 to 2, but a lowernumber of sectors than when the associated codec is one of EVRC modes 5to 7. For example, the maximum-active-sector parameter may be set equalto two for EVRC modes 0 to 2, may be set equal to four for EVRC modes 3and 4, may be set equal to six for EVRC modes 5 to 7.

Additionally or alternatively, the active-set parameter or parametersthat are determined by the RAN may include those that affect how likelya given sector is to be added to or kept in the active set (and thusultimately may affect how many active sectors are in the active set).Such active-set parameters may include, but are not limited to, T_ADD,T_COMP, T_DROP, and/or T_TDROP. In an exemplary embodiment, the RAN mayadjust one or more of these active-set parameters such that a givensector is more or less likely to be added to the active set and/or suchthat a given active sector is more or less likely to be kept in theactive set. In particular, the RAN may decrease T_ADD and/or decreaseT_COMP for a WCD, which may help to increase the probability that agiven sector is added to the active set of the WCD. Additionally oralternatively, the RAN may decrease T_DROP and/or increase T_TDROP,which may help to increase the probability that a given sector is keptin a WCD's active set.

In an exemplary embodiment, method 300 may be implemented so as to takeinto consideration the quality of a WCD's associated codec, when helpingto manage the active set of the WCD. In particular, the RAN may adjustT_ADD, T_COMP, T_DROP, and/or T_TDROP, so as to increase the probabilitythat a new sector is added to a WCD's active set and/or that a givenactive sector is kept in the WCD's active set, when it is determinedthat the codec associated with the WCD is a higher-quality codec.Conversely, the RAN may adjust T_ADD, T_COMP, T_DROP, and/or T_TDROP soas to decrease the probability that a new sector is added to a WCD'sactive set and/or that a given active sector is kept in the WCD's activeset, when it is determined that the codec associated with the WCD is alower-quality codec.

To illustrate an implementation of method 300, FIG. 4 shows a table 400that includes data indicating, for various codecs 402, a correspondingsetting for a maximum-active-sector parameter 404, a corresponding T_ADDsetting 406, and a corresponding T_DROP setting 408. In this example,codecs 402 are identified by EVRC-NW COP values. Eachmaximum-active-sector parameter 402 indicates a maximum number ofsectors that can be included in the WCD's active set. Further, T_ADD andT_DROP are indicated as the Ec/Io value at which a sector is eligible tobe added to or dropped from the active set, respectively.

Once a RAN component (e.g., a base station or a switch) has determinedthe codec that is associated with a WCD, the RAN component may accessdata such as that stored in table 400 to determine the appropriatesettings for one or more active-set parameters. In particular, if a RANcomponent determines that the associated codec is any of COP 5 to COP 8,then based on table 400, the RAN component will set themaximum-active-sector parameter equal to 4, set T_ADD equal to −14, andset T_DROP equal to −17. If, however, the WCD determines that theassociated codec is COP 4, then this means there is a less of a need forthe WCD to be handed off to another coverage area (where it wouldhopefully be assigned a higher-quality codec), than when the associatedcodec is any of COPs 5 to 8. Thus, if the RAN component determines thatthe associated codec is COP 4, then table 400 indicates that themaximum-active-sector parameter should be set to 4, that T_ADD should beset equal to −14, and that T_DROP should be set equal to −17. Thus,while T_ADD and T_DROP remain set in the same manner as for COPs 5 to 8,the maximum number of active sectors is reduced from 6 to 4.

Table 400 also indicates that the probability of a handoff should bereduced further for COPs 1 to 3, and even further for COP 0. Inparticular, the 50-70% range, and then below 50%. In particular, if theassociated codec is any of COPs 1 to 3, then table 400 indicates thatthe maximum-active-sector parameter should be set to 3, that T_ADDshould be set to −13, and that T_DROP should set to −16. And, if theassociated codec is COP 0, then table 400 indicates that themaximum-active-sector parameter should be set to 2, that T_ADD should beset to −12, and that T_DROP should again be set to −16.

It should be understood that the specific codecs 402 and/or thecorresponding values of the active-set parameters 404 to 408 may be varywithout departing from the scope of the invention. Furthermore, itshould be understood that the combination of active-set parameters shownin table 400 is but one example, and that similar data may be providedfor other combinations of one or more active-set parameters withoutdeparting from the scope of the invention.

C. Sending the Message to Indicate Adjusted Active-Set Parameters

At block 306, the RAN may send various types of messages to indicate thedetermined value for the at least on active-set parameter. For example,the RAN may indicate the respectively-determined value for each of oneor more active-set parameters in an overhead message, such as in thevarious types of overhead messages that a RAN routinely sends to a WCDthat is operating in a coverage area of the RAN. The RAN couldadditionally or alternatively indicate the respectively-determined valuefor each of one or more active-set parameters in a system parametersmessage or a handoff direction message (HDM). The RAN could alsoindicate the respectively-determined value for each of one or moreactive-set parameters in other types of messages.

Note that a RAN may or may not send a message indicating the determinedvalue(s) for active-set parameter(s), each time method 300 is performed.In particular, if method 300 is performed and the determined value(s)are no different than the value(s) that were already set for theparticular WCD, then there may not be a need to indicate thenewly-determined value(s) to the WCD. Accordingly, the RAN may refrainfrom explicitly indicating the newly-determined value(s) to the WCD.However, it is also possible that the RAN may send a WCD a messageindicating the determined value(s) for active-set parameter(s), everytime method 300 is performed on behalf of the WCD.

Note that in some instances, a RAN could locally update an active-setparameter that affects whether or not a given sector is included in theactive set of a certain WCD, without explicitly sending a message to theWCD. Thus, block 306 might involve an implicit or indirect indication ofthe determined value for the at least on active-set parameter. Forexample, a RAN could adjust T_COMP locally, in which case block 306might simply involve the RAN sending a Handoff Direction Message (HDM)to the WCD, listing the pilot of a sector that was added based on theadjusted T_COMP as a new member of the active set. Other examples arealso possible.

VI. EXEMPLARY WCD-IMPLEMENTED METHODS

In some embodiments, a WCD may implement an exemplary method in order tomanage its active set based on its assigned codec. For example, when aWCD receives a message indicating that it has been assigned a certaincodec, the WCD may adjust one or more active-set parameters that affectthe (possibly overriding settings that were determined and indicated tothe WCD by the RAN).

FIG. 5 is a flow chart illustrating a method 500 that may be implementedby a WCD, according to an exemplary embodiment. More specifically,method 500 involves a WCD determining a codec that is assigned with theWCD, as shown by block 502. The WCD may then use the assigned codec as abasis for determining a value for at least one active-set parameter thataffects how many active sectors that are included in an active set ofthe WCD, as shown by block 504. The WCD may then manage its active setaccording to the at least one active-set parameter, as shown by block506.

In a further aspect, a WCD may responsively perform method 500 wheneverit receives a message that assigns a codec to the WCD. However, a WCDmay perform method 500 at other times, without departing from the scopeof the invention.

Further, at block 504, the WCD may determine values for one or more ofthe same active-set parameters as described in reference to block 304 ofmethod 300. And, at block 506, the WCD may manage its active set invarious ways, such as those described herein.

VII. CONCLUSION

It should be understood the arrangements and functions described hereinare presented for purposes of example only, and that numerous variationsare possible. For instance, elements can be added, omitted, combined,distributed, reordered, or otherwise modified. Further, where thisdocument mentions functions that can be carried out by a device or otherentity, it should be understood that the functions may be implemented bysoftware (e.g., machine language instructions stored in data storage andexecutable by a processor), firmware, and/or hardware.

I claim:
 1. A method comprising: a radio access network (RAN)determining a codec that is associated with a wireless communicationdevice (WCD); using the associated codec as a basis for determining avalue for at least one active-set parameter for the WCD, whereindetermining the value for at least on active-set parameter comprisesdetermining a value for at least one active-set parameter affectingwhether or not a given sector is included in the active set; and sendinga message to the WCD, wherein the message indicates the determined valuefor the at least one active-set parameter.
 2. The method of claim 1,wherein sending the message to the WCD comprises sending one of: (a) anoverhead message, (b) a system parameters message and (c) a handoffdirection message.
 3. The method of claim 1, wherein the method iscarried out by a base station in the radio access network.
 4. The methodof claim 1: wherein determining the codec that is associated with theWCD comprises determining a codec that was last assigned to the WCD; andwherein using the associated codec as a basis for determining the valuefor the at least one active-set parameter comprises using thelast-assigned codec as a basis for determining the value for the atleast on active-set parameter.
 5. The method of claim 1, whereindetermining a codec that is associated with the WCD comprisesdetermining a codec that is currently assignable to the WCD in a givencoverage area.
 6. The method of claim 5, wherein thecurrently-assignable codec is determined based at least in part onnetwork utilization in the given coverage area.
 7. The method of claim5, wherein the method is carried out by the RAN as part of acall-origination process, and wherein sending the message to the WCDcomprises sending a call registration message to the WCD.
 8. The methodof claim 1, wherein using the determined codec as a basis fordetermining the value for at least on active-set parameter comprisesdetermining, based at least in part on the determined codec, a value ofa maximum-active-sector parameter for the WCD.
 9. The method of claim 8,wherein a plurality of codecs that are available for assignment compriseat least a first and a second codec, wherein the first codec providesfor higher-quality voice service as compared to the second codec, andwherein determining the value of a maximum-active-sector parameter forthe WCD comprises: if the WCD is associated with the first codec, thensetting the value of the maximum-active-sector parameter to a firstvalue; and if the WCD is associated with the second codec, then settingthe value of the maximum-active-sector parameter to a second value,wherein the second value is greater than the first value.
 10. The methodof claim 8, wherein a plurality of codecs that are available forassignment, wherein the plurality of available codecs comprises one ormore first codecs, one or more second codecs, and one or more thirdcodecs, wherein one or more first codecs provide for higher-qualityvoice service as compared to the one or more second codecs, wherein theone or more second codecs provide for higher-quality voice service ascompared to the one or more third codecs, and wherein determining thevalue of a maximum-active-sector parameter for the WCD comprises: if theWCD is associated with one of the first codecs, then setting the valueof the maximum-active-sector parameter to a first value; if the WCD isassociated with one of the second codecs, then setting the value of themaximum-active-sector parameter to a second value, wherein the secondvalue is greater than the first value; and if the WCD is associated withone of the third codecs, then setting the value of themaximum-active-sector parameter to a third value, wherein the thirdvalue is greater than the second value.
 11. The method of claim 10:wherein the one or more first codecs comprise EVRC modes 0 to 2; whereinthe one or more second codecs comprise EVRC modes 3 to 4; wherein theone or more third codecs comprise EVRC modes 5 to 7; and wherein thefirst value is 2, the second value is 4, and the third value is
 6. 12.The method of claim 1, wherein determining the value for the at leastone active-set parameter affecting whether or not a given sector isincluded in the active set comprises at least one of: (a) setting avalue for at least one active-set parameter that affects a probabilitythat a given sector will be added to the active set, (b) setting a valuefor at least one active-set parameter that affects a probability that agiven active sector will be kept in the active set, and (c) setting avalue for at least one active-set parameter that affects a probabilitythat a given active sector will be dropped from the active set.
 13. Themethod of claim 1, wherein determining the value for the at least oneactive-set parameter affecting whether or not a given sector is includedin the active set comprises determining a value for each of one or moreof: (a) a threshold pilot strength for addition to the active set(T_ADD), (b) a threshold difference in signal strength from an activeset pilot (T_COMP), (c) a threshold pilot strength for removal from theactive set (T_DROP), and (d) a time for which an active set pilot fallsbelow T_DROP to justify removal from the active set (T_TDROP).
 14. Aradio-access-network system comprising: a non-transitorycomputer-readable medium; and program instructions stored on thenon-transitory computer-readable medium and executable by at least oneprocessor to: determine a codec that is associated with a wirelesscommunication (WCD); use the associated codec as a basis to determine avalue for at least one active-set parameter for the WCD, wherein the atleast one active-set parameter comprises at least one active-setparameter affecting whether or not a given sector is included in theactive set of the WCD; and send a message to the WCD, wherein themessage indicates the determined value for the at least one active-setparameter.
 15. The system of claim 14, wherein the determined codec is acodec that was last assigned to the WCD.
 16. The system of claim 14,wherein the determined codec is a codec that is currently assignable tothe WCD in a given coverage area.
 17. The system of claim 14, whereinthe at least one active-set parameter for the WCD comprises amaximum-active-sector parameter for the WCD.
 18. A method comprising: awireless communication device (WCD) determining a codec that is assignedto the WCD; using the assigned codec as a basis for determining a valuefor at least one active-set parameter for the WCD, wherein the at leastone active-set parameter affects how many active sectors that areincluded in an active set of the WCD; and managing the active set of theWCD according to the at least one active-set parameter.